An international research team led by scientists from Chengdu University of Technology reports that a series of North Korean underground nuclear test explosions at Mt. Mantap have long-lasting effects on the region’s surrounding crust, including reactivating dormant faults and triggering seismic activity that continues to increase in frequency and magnitude.
Joined by scientists from South Korea’s Pusan National University, the investigators said their research also demonstrates that seismic events created by faults reactivated during these underground nuclear explosions may be difficult to distinguish from naturally occurring tectonic activity.
The researchers suggest their findings could have implications for monitoring former nuclear testing sites.
Seismic Effects of Underground Nuclear Explosions are Poorly Understood
According to a statement announcing the potentially Earth-shaking findings, North Korea’s Punggye-ri test site beneath Mt. Mantap was home to six underground nuclear test explosions between 2006 and 2017. The sixth and final test occurred sometime in September 2017.
Although the North Korean government has not released any information about these tests, the research team behind the new study said the final explosion had an estimated yield of 100 to 250 kilotons. The US Geological Survey (USGS) reported a corresponding magnitude 6.3 seismic event.
When experts examined satellite radar measurements of the site, they found that Mantap’s summit had experienced “substantial ground deformation” after the event.
Because most studies of nuclear test sites focused on strategic information such as yield, location, and timing, the international research team focused on how these massive underground explosions affect the region’s seismic activity, noting that such effects “are poorly understood.”
Test-Induced ‘Aftershocks’ Appear to be Getting Worse
To explore any potential connection, lead author Xingli Fan and colleagues examined seismic activity records collected by nearby South Korean and Chinese monitoring stations. According to the study authors, the stations ranged between 80 and 200kilometers from the North Korean test site.
This analysis revealed 1,399 local earthquakes between 2008 and 2025, the last complete year of data. The researchers said this figure greatly exceeded those recorded in previous catalogs.
When the team narrowed their search to seismic activity in the eight years following the final 2017 test, they found this activity was notably different from seismic activity measured after the previous five underground nuclear test explosions.
For example, typical post-explosion sequences involve a short period of seismic activity followed by a rapid decay back to expected levels. Conversely, seismic activity after the Mt. Mantap test began to spike around three weeks later.
Even more alarming, the researchers said that the increased seismic activity grew in frequency and magnitude right through the end of 2025. The researchers said this suggests the effects of the combined explosion have not diminished but are getting progressively worse.
Effects Hard to Differentiate from Natural Earthquake Activity
A deeper analysis revealed the post-underground nuclear explosion earthquakes were concentrated along two north-northwest-trending fault structures.
The research team said the faults were previously unrecognized, suggesting the explosion caused “persistent and organized fault reactivation,” distinct from naturally occurring seismic activity.
“Repeated nuclear explosions progressively damaged the shallow crust and altered its internal stress field, allowing faults that were already close to failure to become active gradually over several years,” the team’s statement explained.
The team said these events, which may be hard to distinguish from naturally occurring earthquakes, could have potential implications for monitoring former nuclear test sites via their potential effects on the surrounding area’s seismic activity.
The study “Nuclear tests at Mt. Mantap have reactivated intraplate faults” was published in Science.
Christopher Plain has spent the last six years as Associate News Editor and Head Science Reporter at The Debrief. Follow and connect with him on X, learn about his novels at plainfiction.com, or email him at christopher@thedebrief.org.